Suplatast tosilate [(±)-[2-[4-(3-ethoxy-2-hydroxypropoxy) phenylcarbamoyl] ethyl] dimethylsulfonium p-toluenesulfonate] represented by the below-described formula has excellent inhibitory action against IgE antibody formation, is useful as a medication for various allergic diseases such as bronchial asthma, atopic dermatitis and allergic rhinitis and is utilized in the racemate as a pharmaceutical (refer to Japanese Patent Publication No. Hei 3-70698). It is also known that the suplatast tosilate is useful as a medication for dysuria or pruritus associated with kidney dialysis (WO 00/27383, Japanese Patent Laid-Open No. Hei 11-315019).

As the crystal of the racemate of the suplatast tosilate, those prepared by the process as described in Japanese Patent Publication No. Hei 3-70698 and Japanese Patent Laid-Open No. Hei 7-252213 (which crystals will hereinafter be called “first crystal” and “second crystal”, respectively) are known.
The suplatast tosilate first crystal is however a peculiar compound, because its optically active substance ratio fluctuates when re-crystallized at a high concentration as described in Japanese Patent Laid-Open No. Hei 7-300453 or Angew, Chem. Int. Ed. Engl., 35, 2372–2374(1996). Adjustment of the optical active substance ratio within a predetermined range, thereby maintaining its quality as a pharmaceutical requires re-crystallizing operation at a lowered solution concentration, which needs a large amount of a solvent for re-crystallization. Moreover, since re-crystallization at a high concentration causes fluctuations in the optically active substance ratio, the crystal cannot be collected from a re-crystallized mother liquor and the whole amount of the mother liquor is inevitably discarded, which leads to a rise in the manufacturing cost. Another problem is that the crystal whose optically active substance ratio stands outside a predetermined range owing to fluctuations must be discarded. The reason why the first crystal suffers from fluctuations in the optically active substance ratio is not known clearly, but is presumed to owe to crystal growth at a portion undergoing a slight change in the ratio (Refer to, “Kagaku, 54; No. 6, 47–54 (1999)”).
Moreover, high hygroscopicity of suplatast tosilate, both the first crystal and second crystal, disturbs easy handling during a quality test, storage management, or drug preparation step. Described specifically, the water content of the crystal increases during its preparation step, which may change its adhesion property, making it difficult to fill it in capsules or, from the viewpoint of quality management, may cause a drop in melting point owing to moisture absorption, making it nonconforming. It is therefore necessary to severely control the storage environment. The suplatast tosilate second crystal has not yet been developed as a pharmaceutical, because considerably high deliquescence makes it difficult to control its quality.